“We fully recognise the local community will still be concerned and our investigation very much remains active and we will continue to work to identify and seek to arrest all of those who may have been involved,” she added.
The Met previously said the investigation was looking at an Islamist group with potential links to Iran.
Harakat Ashab al-Yamin al-Islamiya – The Islamic Movement of the People of the Right Hand – made an unsubstantiated claim of responsibility for the attack.
The group has claimed responsibility for a number of similar arson incidents across Europe.
Although the case is not being classed as a terror incident, the Met said the investigation is currently being led by counter-terror officers.
The Community Security Trust, a charity that tracks antisemitism in the UK and provides security to British Jews, welcomed the arrests and said: “We are grateful to the officers who have worked tirelessly to find those accountable.
“While this development is an important step forward, we know the community will understandably remain concerned.”
It added that its security operations would remain at a “high level”.